Using Firefox/Introduction

Mozilla Firefox (originally known as "Phoenix" and briefly as "Mozilla Firebird") is a free, cross-platform, graphical web browser developed by the Mozilla Foundation and hundreds of volunteers. Its current release is Firefox 54.0.1, released on June 29, 2017, and ESR (Extended Support Release) build is version 52.2.1, released on June 29, 2017.

Firefox strives to be a lightweight, fast, intuitive, and highly extensible standalone browser. Firefox has now become the foundation's main development focus. Firefox includes an integrated pop-up blocker, tabbed browsing, live bookmarks, built in Phishing protection, support for open standards, an extension mechanism for adding functionality and localization for Firefox in different languages. Firefox also attempts to produce secure software and fix security holes promptly. Although other browsers have introduced these features, Firefox is the first such browser to achieve wide adoption.

Firefox has attracted attention as an alternative to other browsers such as Microsoft's Internet Explorer. Currently, Firefox is the 3rd most popular browser in the world. Since its release, Firefox has significantly reduced Internet Explorer's dominant usage share.

Before its 1.0 release on November 9, 2004, Firefox had already gained acclaim from numerous media outlets, including Forbes and the Wall Street Journal. With over 25 million downloads in the 99 days after its release, Firefox became one of the most downloaded free and open source applications, especially among home users. On October 19, 2005, Firefox had its 100 millionth download, just 344 days after the release of version 1.0. By January 31, 2009 Firefox had been downloaded 1 billion times.

Firefox has become the foundation's main development focus (along with its Thunderbird email client), and has replaced the Mozilla Suite as their official main software release.

Blake Ross began working on the Firefox project as an experimental branch of the Mozilla project. They believed that the commercial requirements of Netscape's sponsorship and developer-driven feature creep compromised the utility of the Mozilla browser. To combat what they saw as the Mozilla Suite's software bloat, they created a pared-down browser (then known as Phoenix, today known as Firefox), with which they intended to replace the Mozilla Suite. Ben Goodger currently works as the lead developer of Firefox.

Mozilla Firefox retains the cross-platform nature of the original Mozilla browser by using the XUL user interface markup language. Through Firefox's support of XUL, users may extend their browser's capabilities by applying themes and extensions. Initially, these add-ons raised security concerns, so with the release of Firefox 0.9, the Mozilla Foundation opened Mozilla Update, a website containing themes and extensions "approved" as not harmful.

Mozilla contributors constantly improve Firefox's support for existing standards. Firefox has already implemented most of CSS Level 2 and some of the not-yet-completed CSS Level 3 standard. Also, work continues on implementing standards currently missing, including APNG and XForms. Some of the Mozilla standards like XBL is also making its way to open standards (via WHATWG).